A Greek rail inspector was detained on Friday in connection with last month's train disaster that killed 57 people, a court official said.
The employee, a station manager supervisor identified as Dimitris Nikolaou, was charged with the crime of "disruption of traffic safety" causing the death of many people, the official said.
He was on duty at the time of the accident on February 28, when a passenger train and a freight train collided head-on after running on the same track for several kilometres near the city of Larissa.
The station master on duty has also been charged and jailed, and faces a life sentence if convicted on charges of endangering public transport and negligent homicide.
But two other rail employees were released on bail earlier this week after testifying.
Railway unions had long warned the network was underfunded, understaffed and accident-prone after a decade of spending cuts.
Greece's rail watchdog earlier this month said it had found serious safety problems across the network, including inadequate basic training for critical staff.
The tragedy is set to weigh heavily on national elections set for May 21, with Prime Minister Kyriakos Mitsotakis seeking re-election on pledges of safety improvements.